The objective of this research program is to define the factors responsible for, and the mechanisms by which, expansion of the adipose tissue and alterations in carbohydrate and lipid metabolism occur in obesity. Adipose cell size and number will be measured in human twins, and in experimental animals undergoing various nutritional and hormonal manipulations during fetal, neonatal, and prepubertal life, in an attempt to assess genetic, dietary and endocrine influences on the normal growth and cellular character of the adipose tissue, and to define the stimuli responsible for adipose hypercellularity in obesity. Glucose and lipid metabolism of and the response to insulin and epinephrine by adipose tissue from nonobese and obese man and experimental animal will be studied as a function of adipose cell size, dietary intake and the state of growth and physical activity of the organism. Particular emphasis will be directed towards integrative studies of the metabolism of the whole cell and its cell membrane and intracellular functions. The in vitro metabolism of adipose tissue will be correlated with simultaneous in vivo measurements of these parameters of metabolism in the plasma, forearm tissues and other tissues of man and experimental animal. The relationship between eating behavior and these morphologic and metabolic characteristics, and the influence upon various programs of weight reduction upon this behavior will be studied.